Automated data storage libraries represent a significant investment and a significant proportion of any large data processing complex. For example, in many complexes, the automated data storage libraries represent a majority of the cost of the entire complex. Thus, it is desirable to update libraries and utilize the same storage slots and cartridge handling apparatus rather than to replace the libraries.
The conventional approach to update tape automated data storage libraries is to increase the amount of data stored in each portable container of recording tape by increasing the length of tape by reducing its thickness and/or by increasing the track density and the linear data density of data stored on the tape. The tape head in the data storage drive in an automated data storage library may have to be altered to handle the thinner tape, and has to be altered in each instance of a change in data density in order to handle the increased number of tracks and the increased linear data density, but the same automated cartridge handling apparatus and the same storage slots continue to be utilized. An example of such an automated data storage system comprises the 3495 Automated Dataserver Library.
A more important measure of the performance of an automated data storage library than the absolute capacity is the throughput of the library. A key factor in throughput is the time to data. However, as the amount of data stored in each cartridge or cassette is increased, the speed of accessing that increased data by the library tape drive is often not similarly increased. If the length of the recording tape is increased, the speed of accessing that data may decrease as the time required by the tape drive to wind the tape spools increases to move the desired data to the tape head, thereby increasing the time required to gain access to data on the longer tape.